T cell mediated metal hypersensitivity is wide spread in the human population. Two examples are hypersensitivity to nickel (Ni) often associated with exposure to Ni contained jewelry and to beryllium (Be) a common problem in the industries that work with this metal and sometimes resulting in a serious inflammatory lung disease, chronic berylliosis disease (CBD). How these metals become part of a ligand for a|3 T cell receptors is unknown. The conventional wisdom is that by some means ions of these metal behave like haptens, i.e. they find a place to bind on the face of MHC molecules (with or without a contribution from the bound peptide), such that they become an integral part of the interface during a(3TCR engagement. This can be thought of as a post translational modification that converts a self antigen into a foreign antigen post self-tolerance and, therefore, may be relevant to other types of peptide post translational modification with potential to induce autoimmunity We propose to study the mechanism of T cell mediated Ni and Be recognition by CD4 T cells. In both cases our goal will be to understand the structural nature of the metal containing ligand of the a(3TCR of a metal reactive human T cell. Our hypothesis is that there are a limited set of ways in which metal can incorporate themselves into a T cell ligand and that through our studies will be able to discern the general rules. The T cells that we will study require a particular MHCII molecule (either DR52c or DP2) with a specific, but unknown, bound peptide in order to recognize the presented Ni or Be, respectively. We have developed a baculovirus mediated display method for producing large libraries of MHC bound peptides expressed on the surface of virally infected insect cells, such that each cell expresses MHC bound to one peptide variant in the library. With these infected cells as fish and multimeric, fluorescent, soluble a|3TCRs as bait, we will use flow cytometric sorting to identify and isolate DR52c or DP2 bearing peptide "mimotopes" that satisfy the metal presentation requirements of the Ni and Be reactive T cells. We will then determine the structures of these MHCII/mimotope complexes with and without the bound metal ion. We will also determine the structures of the apTCRs bound to these complexes. While the concepts and details of T cell recognition of peptides that result from the degradation of self and foreign proteins are well established, very little is known about how non-peptide chemicals can be recognized by T cells. Our experiments will not only have implications for understanding metal hypersensitivity to Ni jewelry and to Be in the workplace, but may be relevant to understanding metal sensitivity in other settings such as colloidal gold treatment of arthritis and metal containing prostheses.